Low threshold mos two phase negative charge pump

Abstract

A triple well charge pump comprises a first transistor connected in a diode configuration having a first channel terminal, nominally the source, coupled to a first node, and the second channel terminal, nominally the drain, coupled to its gate and to a second node. A first capacitor has a first terminal coupled to the first node of the charge pump, and a second terminal adapted to receive a first clock signal. A second transistor has a first channel terminal coupled to the second node of the charge pump, and a second channel terminal coupled to its gate and to a third node. A second capacitor has a first terminal coupled to the second node, and a second terminal adapted to receive a second clock signal. The first and second transistors comprise a first region and a second region having a first conductivity type providing the first and second channel terminals respectively, a channel region in which the first and second regions are formed having a second conductivity type, and an isolation well having the first conductivity type in a semiconductor substrate. The first and second regions, the channel region and the isolation well form a parasitic bipolar junction transistor that has a threshold voltage. The channel region has a doping concentration establishing a threshold voltage for the MOS transistor which is less than the threshold voltage of the parasitic bipolar junction transistor. The clock signals have sloped rising and falling edges.